The present invention relates to a new gas turbine for power generation, which is capable of enhancing the heat efficiency by increasing a turbine inlet temperature up to 1200xc2x0 C. or more, and a combined power generation system using the gas turbine.
In recent years, it is expected to improve the heat efficiency of a gas turbine from the viewpoint of energy saving. To improve the heat efficiency of a gas turbine, it is most effective to increase the gas temperature and gas pressure thereof. For example, by increasing the gas temperature from 1200xc2x0 C. to 1650xc2x0 C. and also increasing the gas compression ratio to about 15, it is possible to make the heat efficiency larger than that of the conventional gas turbine operated at 1200xc2x0 C. or less by about 3% or more.
Along with the increases in gas temperature and gas compression ratio, however, it is required to use materials having higher strengths, particularly, higher creep rupture strengths which exert the largest effect on the high temperature characteristics of the materials. In general, an austenite steel, an Ni-based alloy, a Co-based alloy, and a martensite steel are known as structural materials higher in creep rupture strength. Of these materials, the Ni-based alloy and Co-based alloy are undesirable in terms of hot workability, machinability, and vibration damping property; and the austenite steel is also undesirable in terms of poor high-temperature strength at a temperature ranging from 400 to 450xc2x0 C. and of matching with the entire material configuration of the gas turbine. On the other hand, the martensite steel is desirable in matching with materials of other components of the gas turbine and also sufficient in high-temperature strength. The use of the martensite steel has been known, for example, from Japanese Patent Laid-open Nos. Sho 63-60262 and Hei 5-263657. The martensite steel disclosed in these documents, however, is not necessarily high in creep rupture strength at a temperature ranging from 400 to 500xc2x0 C., and therefore, it cannot be used as the material as it is for a turbine disk or the like provided in a gas turbine operated at a high temperature.
To meet the requirement to increase the gas temperature and gas pressure of a gas turbine, it is insufficient to use materials which are only high in strength. To be more specific, to cope with the tendency to increase the gas temperature of a gas turbine, it is required to use heat-resistant materials which are high not only in strength but also in toughness. In general, however, if the strength of a material is increased, the toughness thereof is reduced.
Accordingly, it is generally difficult to obtain a martensite steel which is high in both strength and toughness.
An object of the present invention is to provide a gas turbine for power generation, which is improved to increase the heat efficiency and also increase the gas temperature by combination of the use of a material high in both strength and toughness and a technique of cooling the gas turbine, and to provide a combined power generation system of the gas turbine and a steam turbine combined therewith.
According to the present invention, there is provided a gas turbine for power generation, including a compressor, a combustor, three stages or more turbine blades fixed to turbine disks, and three stages or more turbine nozzles provided in matching with the turbine blades, characterized in that the gas turbine has an air cooling line for cooling the turbine disks in a range from shells of the turbine disks to the turbine blades by using air compressed by the compressor; and the turbine disks are each made from a martensite steel.
According to the present invention, there is also provided a gas turbine for power generation, including a compressor, a combustor, three stages or more turbine blades fixed to turbine disks, and three stages or more turbine nozzles provided in matching with the turbine blades, characterized in that the gas turbine has a steam cooling line for cooling the turbine disks in a range from shells of the turbine disks to the turbine blades by using steam; and the turbine disks are each made from a martensite steel.
According to the present invention, there is also provided a gas turbine for power generation, including a compressor, a combustor, three stages or more turbine blades fixed to turbine disks, and three stages or more turbine nozzles provided in matching with.the turbine blades, characterized in that a gas temperature at the inlet of the first stage turbine nozzle is in a range of 1200 to 1650xc2x0 C.; the gas turbine has an air cooling line for cooling the first stage turbine nozzle and also cooling the first and second stage turbine disks in a range from shells of the first and second stage turbine disks to the first and second stage turbine blades by using air compressed by the compressor and cooled by a cooler; the gas turbine further has an air cooling line for cooling the second and third stage turbine nozzles by using air; and the turbine disks are each made from a martensite steel.
According to the present invention, there is also provided a gas turbine for power generation, including a compressor, a combustor, three stages or more turbine blades fixed to turbine disks, and three stages or more turbine nozzles provided in matching with the turbine blades, characterized in that a gas temperature at the inlet of the first stage turbine nozzle is in a range of 1200 to 1650xc2x0 C.; the gas turbine has a steam cooling line for cooling the first stage turbine nozzle and also cooling the first and second stage turbine in a range from shells of the first and second stage turbine disks to the first and second stage turbine blades by using steam; the gas turbine further has an air cooling line for cooling the second and third stage turbine nozzles by using air; and the turbine disks are each made from a martensite steel.
The above-described gas turbine for power generation is preferably configured such that the gas temperature at the inlet of the first stage turbine nozzle is in a range of 1200 to 1295xc2x0 C.; and the martensite steel contains, on the weight basis, 0.05-0.20% of C, 0.15% or less of Si, 1.0% or less of Mn, 0.50-3.0% of Ni, 8.0-13.0% of Cr, 1.0-4.0% of Mo, 0.10-0.40% of V, and 0.025-0.125% of N.
The gas turbine for power generation is also preferably configured such that the gas temperature at the inlet of the first stage turbine nozzle is in a range of 1300 to 1395xc2x0 C.; and the martensite steel contains, on the weight basis, 0.05-0.20% of C, 0.15% or less of Si, 1.0% or less of Mn, 0.50-3.0% of Ni, 8.0-13.0% of Cr, 1.0-4.0% of Mo, 0.10-0.40% of V, 0.01-0.20% of Nb, and 0.025-0.125% of N.
The gas turbine for power generation is also preferably configured such that the gas temperature at the inlet of the first stage turbine nozzle is in a range of 1400 to 1650xc2x0 C.; and the martensite steel contains, on the weight basis, 0.05-0.20% of C; 0.15% or less of Si; 0.20% or less of Mn; 0.5-3.0% of Ni, preferably, 0.50-2.50% of Ni; 8.0-13.0% of Cr, preferably, 10.5-12.5% of Cr; 1.0-4.0% of Mo, preferably, 1.7-2.1% of Mo; 0.10-0.40% of V, preferably, 0.15-0.25% of V; 0.01-0.20% of Nb, preferably, 0.06-0.12% of Nb; 0.025-0.125% of N, preferably, 0.025-0.070% of N; and 1.0-5.0% of Co. When the gas inlet temperature is in the above range of 1400 to 1650xc2x0 C., the temperature of the first stage turbine disk is increased to about 500xc2x0 C.; however, the first stage turbine disk, which is made from the above martensite steel, sufficiently withstands such a high temperature. Although the temperature of each of the second and third stage turbine disks is slightly lower than that of the first stage turbine disk, it reaches 450xc2x0 C. or more.
The martensite steel, used in either of the above three temperature ranges, preferably further contains one kind or more of 0.2-2.0% of W and 0.0005-0.010% of B. The above martensite steel can be used for at least one of a distant piece, a turbine spacer, a final stage compressor disk, a turbine stacking bolt, and a compressor stacking bolt, complying with any one of the above three temperature ranges.
The above-described martensite steel is preferably configured such that the ratio (Mn/Ni) is in a range of 0.11 or less; the content of (Mn+Ni+Co) is in a range of 2.0 to 7.0%; the content of (Mo+0.5W) is in a range of 1.0 to 2.0%; the Cr equivalent expressed by (Cr+6Si+4Mo+1.5W +11V+5 Nbxe2x88x9240Cxe2x88x9230Nxe2x88x922Mnxe2x88x924Ni xe2x88x922Co) is 8 or less; and the contents of impurities are limited as follows; 0.030% or less of P, 0.010% or less of S, 0.0030% or less of H, and 0.020% or less of O.
According to the present invention, there is also provided a combined power generation system in which a generator is driven by a gas turbine driven by a combustion gas flowing at a high speed, an exhaust gas heat recovery boiler for obtaining steam by using an energy of exhaust gas discharged from the gas turbine, and a high pressure-low pressure integral type steam turbine and a gas turbine, characterized in that the gas turbine is composed of the above-described gas turbine for power generation.
According to the present invention, there is also provided a combined power generation system in which a generator is driven by a high pressure-low pressure integral type steam turbine and a gas turbine, characterized in that a steam temperature at the inlet of a first stage nozzle of the steam turbine and a gas temperature at the inlet of a first stage nozzle of the gas turbine are in a range defined by connecting points A (515xc2x0 C., 1200xc2x0 C.), points B (538xc2x0 C., 1200xc2x0 C. ), points C (593xc2x0 C., 1650xc2x0 C. ), and points D (557xc2x0 C., 1650xc2x0 C.) to each other; and the gas turbine includes a compressor; a combustor; three stages or more turbine blades fixed to turbine disks, three stages or more turbine nozzles provided in matching with the turbine blades; an air cooling line for cooling the first stage turbine nozzle and the first and second stage turbine blades by using air compressed by the compressor and cooled by a cooler, or a steam cooling line for cooling the first stage turbine nozzle and the.first and second stage turbine blades by using steam; and an air cooling line for cooling the second and third stage turbine nozzles by using air.
According to the present invention, there is also provided a combined power generation system in which a generator is driven by a high pressure-low pressure integral type steam turbine and a gas turbine, characterized in that a steam temperature at the inlet of a first stage nozzle of the steam turbine and a gas temperature at the inlet of a first stage nozzle of the gas turbine are in a range defined by connecting to each other on a steam temperature/gas temperature diagram points A (515xc2x0 C., 1200xc2x0 C.), points B (538xc2x0 C., 1200xc2x0 C.), points C (593xc2x0 C., 1650xc2x0 C.), and points D (557xc2x0 C., 1650xc2x0 C.) to each other; and the gas turbine includes a compressor; a combustor; three stages or more turbine blades fixed to turbine disks, three stages or more turbine nozzles provided in matching with the turbine blades; an air cooling line for cooling the first stage turbine nozzle and the first and second stage turbine blades by using air compressed by the compressor and cooled by a cooler, or a steam cooling line for cooling the first stage turbine nozzle and the first and second stage turbine blades by using steam; and an air cooling line for cooling the second and third stage turbine nozzles by using air.
The above high pressure-low pressure integral type steam turbine is preferably configured such that a value of xe2x80x9cblade portion length (inches)xc3x97rotational number (rpm)xe2x80x9d of the final stage turbine blade is in a range of 120000 or more; and the final stage turbine blade of the steam turbine is made from a martensite steel.
The gas turbine of the present invention is also preferably configured such that at least one of the first stage turbine blade and the first stage turbine nozzle is made from an Ni-based alloy having a single crystal if used at the above gas inlet temperature ranging from 1400 to 1650xc2x0 C., or is made from an Ni-based alloy having a columnar crystal structure if used at the above gas inlet temperature ranging from 1300 to 1395xc2x0 C.
The gas turbine of the present invention is also preferably configured such that if used at the above gas inlet temperature ranging from 1400 to 1650xc2x0 C., the second and third stage turbine blades are each made from a unidirectionally solidified Ni-based alloy having a columnar crystal structure.
The gas turbine of the present invention is also preferably configured such that if used at the above gas inlet temperature ranging from 1400 to 1650xc2x0 C., the first stage turbine blade and the first stage turbine nozzle are each made from an Ni-based alloy having a single crystal structure;at least one of the second and third stage turbine blades is made from a unidirectionally solidified Ni-based alloy having a columnar crystal structure; and the second and third stage turbine nozzles-are each made from an Ni-based alloy having an equi-axed crystal structure.
The martensite steel according to the present invention is used for at least a turbine disk, and can be similarly used for at least one of a distant piece, a turbine spacer, a final stage compressor disk, and a turbine staking bolt. The reason why the content range of each element of the martensite steel is limited will be described below. The content of C is preferably in a range of 0.05% or more for enhancing the tensile strength and yield strength of the martensite steel. However, if the content of C becomes excessively large, the metal structure becomes unstable when the martensite steel is exposed to a high temperature environment for a long time, with a result that the 105 h creep rupture strength of the martensite steel is reduced. Accordingly, the upper limit of the C content is preferably set at 0.20%. The C content is preferably in a range of 0.07 to 0.15%, more preferably, in a range of 0.10 to 0.14%.
The elements Si and Mn are respectively added as a deoxidizer and a deoxidizer/desulfurizer upon melting of steel. The effect of adding Si or Mn can be obtained only by addition of a slight amount thereof. However, since Si is the element of assisting the generation of a xcex4-ferrite phase, the addition of a large amount of Si accelerates the generation of the xcex4-ferrite phase which triggers reduction in the fatigue strength and the toughness of the material. Accordingly, the content of Si is preferably in a range of 0.5% or less. If the raw material is melted by a carbon vacuum deoxidizing process and an electro-slag melting process, it is not required to add Si, and it is rather desirable not to add Si. In particular, the Si content is preferably in a range of 0.2% or less to prevent occurrence of embrittlement of the martensite steel. In the case of no addition of Si, the Si content is preferably limited to 0.05% or less.
Mn is the element of accelerating the embrittlement of the martensite steel due to heating, and therefore, the content of Mn is preferably in a range of 0.6% or less. In particular, since Mn is effective as a deoxidizer, it may be added in a range of 0.05 to 0.4%, preferably, 0.05 to 0.25% in consideration of preventing occurrence of embrittlement due to heating. The content of (Si+Mn) is preferably in a range of 0.3% or less from the viewpoint of preventing the embrittlement of the martensite steel.
Cr is effective to enhance the corrosion resistance; and high-temperature strength; however, if Cr is added in an amount of 13% or more, it causes the generation of a xcex4-ferrite structure. On the other hand, if :the content of Cr is less than 8%, the effect of enhancing-the corrosion resistance and high-temperature strength cannot be sufficiently achieved. Accordingly, the Cr content is preferably in a range of 8 to 13%, more preferably, 10.5 to 12.5% from the viewpoint of improvement of the high-temperature strength.
Mo is effective to enhance the creep rupture strength due to the function of reinforcing solid-solution and precipitation and also to prevent occurrence of embrittlement. To ensure a high creep rupture strength, Mo is preferably added in an amount of 1.0% or more; however, if Mo is added in an amount of 4.0% or more, it causes the generation of the xcex4-ferrite phase. Accordingly, the Mo content is preferably in a range of 1.0 to 4.0%, more preferably, 1.8 to 2.5%. Additionally, in the case where the Ni content is more than 2.1%, the larger the Mo content, the larger the effect of enhancing the creep rupture strength. In particular, such an effect becomes large when the Mo content is in a range of 2.0% or more.
V and Nb are effective to precipitate carbides for enhancing the high-temperature strength and also to improve the toughness. The content of V is preferably in a range of 0.1% or more, and the content of Nb is preferably in a range of 0.01% or more. The addition of V in an amount of 0.4% or more and Nb in an amount of 0.2% or more is undesirable because it causes the generation of the xcex4-ferrite phase and tends to reduce the creep rupture strength. Accordingly, the V content is preferably in a range of 0.15 to 0.25%, and the Nb content is preferably in a range of 0.04 to 0.10%. Ta may be added in place of Nb or in combination of Nb.
Ni is effective to enhance the toughness after the material is heated at a high temperature for a long time, and to prevent the generation of the xcex4-ferrite phase. To achieve the above effect, the content of Ni is preferably in a range of 0.5% or more; however, the addition of Ni in an amount of more than 3% is undesirable because it reduces the long-period creep rupture strength. Accordingly, the content of Ni is preferably in a range of 2.0 to 3.0%, more preferably, 2.5 to 3.0%.
Although Ni is effective to prevent the embrittlement of the material due to heating, Mn tends to exert adverse effect. Accordingly, from the viewpoint of embrittlement due to heating, there is a close relationship between Ni and Mn. By setting the ratio (Mn/Ni) at 0.11 or less, it is possible to significantly prevent the embrittlement due to heating. In particular, the ratio (Mn/Ni) is, preferably, in a range of 0.10 or less, more preferably, 0.04 to 0.10.
N is effective to improve the creep rupture strength and to prevent the generation of the xcex4-ferrite phase. The content of N is preferably in a range of 0.025% or more; however, if N is added in an amount of more than 0.125%, it reduces the toughness. In particular, to obtain excellent characteristics, the content of N is preferably in a range of 0.03 to 0.08%.
Co is effective to enhance the high-temperature strength. To improve the high-temperature characteristics of the material, it is desirable to increase the content of Co. Concretely, Co is preferably added in an amount of 1.0 to 5.0%.
Like the above-described element Mo, W contributes to the reinforcement of the material. The content of W is preferably in a range of 0.2 to 2.0%. B has an effect of significantly reinforcing the material. The content of B is preferably in a range of 0.0005 to 0.01%. Further, by adding 0.3% or less of Al, 0.5% or less of Ti, 0.1% or less of Zr, 0.1% or less of Hf, 0.01% or less of Ca, 0.01% or less of Mg, 0.01% or less of Y, 0.01% or less of a rare earth element, and 0.5% or less of Cu, the high-temperature strength of the martensite steel can be improved.
The heat-treatment of the steel of the present invention is preferably performed by uniformly heating the steel material at a temperature ranging from 900 to 1150xc2x0 C. to transform the metal structure into an austenite structure, rapidly cooling the material at a cooling rate of 100xc2x0 C./h or more to transform the austenite structure to a martensite structure, heating and keeping the material to and at a temperature ranging from 450 to 600xc2x0 C. (primary tempering), and heating and keeping the material to and at a temperature ranging from 550 to 650xc2x0 C. (secondary tempering). The quenching temperature is preferably set at a temperature right over the Ms point, for example, 150xc2x0 C. or more, for preventing occurrence of quenching cracks. The quenching is preferably performed by an oil quenching or water atomization quenching method. The primary tempering is performed by heating the material from the quenching temperature to a temperature ranging from 450 to 600xc2x0 C.
With respect to multi-stage compressor disks, at least the final stage disk or all of the disks can be made from the above heat resisting steel. Alternatively, the disks, disposed on the upstream side (low gas temperature side) from the first stage disk to an intermediate stage disk, can be made from a low alloy steel, and the disks on the downstream side from the intermediate stage disk to the final stage disk can be made from the above heat resisting steel. The disks on the upstream side from the first stage disk to the intermediate stage disk may be made from an Nixe2x80x94Crxe2x80x94Moxe2x80x94V steel which contains, on the weight basis, 0.15-0.30% of C, 0.5% or less of Si, 0.6% or less of Mn, 1-2% of Cr, 2.0-4.0% of Ni, 0.5-1% of Mo, and 0.05-0.2% of V, the balance being substantially Fe, and which exhibits the tensile strength at room temperature in a range of 80 kg/mm2 or more and the V-notch Charpy impact value at room temperature in a range of 20 kg-m/cm2 or more. The disks on the downstream side from the intermediate stage disk, excluding at least the final stage disk, may be made from a Crxe2x80x94Moxe2x80x94V steel which contains, on the weight basis, 0.2-0.4% of C, 0.1-0.5% of Si, 0.5-1.5% of Mn, 0.5-1.5% of Cr, 0.5% or less of Ni, 1.0-2.0% of Mo, and 0.1-0.3% of V, the balance being substantially Fe, and which exhibits the tensile strength at room temperature in a range of 80 kg/mm2 or more, the elongation percentage in a range of 18% or more, and the percentage of reduction of area in a range of 50% or more.
A compressor stub shaft can be made from an Nixe2x80x94Crxe2x80x94Moxe2x80x94V steel containing, on the weight basis, 0.15-0.3% of C, 0.5% or less of Si, 0.6% or less of Mn, 2-4% of Ni, 1-2% of Cr, 0.5-1% of Mo, and 0.05-0.2% of V. A turbine stub shaft can be made from a Crxe2x80x94Moxe2x80x94V steel containing, on the weight basis, 0.2-0.4% of C, 0.1-0.5% of Si, 0.5-1.5% of Mn, 0.5-1.5% of Cr, 0.5% or less of Ni, 1-2% of Mo, and 0.1-0.3% of V.
In the case of compressor disks comprising seventeen stages, the disks in the first to twelfth stages can be each made from the above-described Nixe2x80x94Crxe2x80x94Moxe2x80x94V steel; the disks in the thirteenth to sixteenth stages can be each made from the Crxe2x80x94Moxe2x80x94V steel; and the disk in the seventeenth stage can be made from the above-described martensite steel.
The first and final compressor disks have structures that the disk next to the first stage compressor disk has a rigidity and the disk immediately preceding to the final stage compressor disk has a rigidity. These disks are also configured such that the thickness of each disk becomes smaller in the direction from the first stage to the final stage.
The blades and nozzles of the compressor are each preferably made from a martensite steel containing 0.05-0.2% of C, 0.5% or less of Si, 1% or less of Mn, 10-13% of Cr or 0.5% or less of Mo, and 0.5% or less of Ni, the balance being Fe.
With respect to shrouds each of which is brought into slide-contact with the tip of the turbine blade and is formed into a ring-shape, the first stage shroud can be made from a cast alloy containing, on the weight basis, 0.05-0.2% of C, 12% or less of Si, 2% or less of Mn, 17-27% of Cr, 5% or less of Co, 5-15% of Mo, 10-30% of Fe, 5% or less of W, and 0.02% or less of B, the balance being substantially Ni; and the remaining shrouds can be each made from a cast alloy containing, on the weight basis, 0.3-0.6% of C, 2% or less of Si, 2% or less of Mn, 20-27% of Cr, 20-30% or less of Ni, 0.1-0.5% of Nb, and 0.1-0.5% of Ti, the balance being substantially Fe. Such a shroud is composed of a plurality of blocks formed into the ring-shape.
With respect to the diaphragms for fixing the turbine nozzles, the first stage turbine nozzle can be made from an alloy containing, on the weight basis, 0.05% or less of C, 1% or less of Si, 2% or less of Mn, 16-22% of Cr, and 8-15% of Ni, the balance being substantially Fe; and the remaining turbine nozzle portion can be each made from a high C-high Ni steel casting.
A plurality of combustors are arranged around the turbine. Each combustor has a double structure of an outer cylinder and an inner cylinder. The inner cylinder can be made from an alloy containing, on the weight basis, 0.05 to 0.2% of C, 2% or less of Si, 2% or less of Mn, 20-25% of Cr, 0.5-5% of Co, 5-15% of Mo, 10-30% of Fe, 5% or less of W, and 0.02% or less of B, the balance being substantially Ni. The inner cylinder is obtained by bending a plate (thickness: 2-5 mm) and welding both ends of the plate, and crescent louver holes for supplying air are formed over the periphery of the cylinder. The material is subjected to solution treatment to have an austenite structure.
A turbine blade used for a condition in which the combustion gas temperature at the inlet of a turbine nozzle is in a range of 1200 to 1295xc2x0 C. can be made from an ordinary cast alloy which contains, on the weight basis, one or more kinds of 0.07-0.25% of C, 1% or less of Si, 1% or less Mn, 12-20% of Cr, 5-15% of Co, 1.0-5.0% of Mo, 1.0-5.0% of W, 0.005-0.03% of B, 2.0-7.0% of Ti, 3.0-7.0% of Al, 1.5% or less of Nb, 0.01-0.5% of Zr, and 0.01-0.5% of Hf, 0.01-0.5% of V, the balance being substantially Ni, and which has a structure in which a xcex3xe2x80x2-phase and a xcex3xe2x80x3-phase are precipitated in an austenite phase matrix. A turbine nozzle can be made from a cast alloy which contains, on the weight basis, 0.20-0.60% of C, 2% or less of Si, 2% or less of Mn, 25-35% of Cr, 5-15% of Ni, 3-10% of W, and 0.003-0.03% of B, the balance being substantially Co, and further contains, if needed, at least one kind of 0.1-0.3% of Ti, 0.1-0.5% of Nb, and 0.1-0.3% of Zr, and which has a structure in which eutectic carbides and secondary carbides are precipitated in an austenite phase matrix. These alloys are each subjected to solution treatment and aging treatment to form the above-described precipitates for reinforcing the structure.
To prevent corrosion due to high temperature combustion gas, the turbine blade can be covered with a diffusion coating of Al, Cr, or (Al+Cr). The thickness of the coating layer is preferably in a range of 30 to 150 xcexcm. The coating layer is preferably formed on a blade portion being in contact with gas.
For the 1300xc2x0 C.-class gas turbine for power generation and the next generation 1500xc2x0 C.-class gas turbine for power generation, the metal temperature of the first stage turbine blade reaches up to 700xc2x0 C. or more and further sometimes reaches up to 900xc2x0 C. or more even in the consideration of the cooling technique. Accordingly, the material used for such a first stage blade is required to exhibit a useful temperature higher than the metal temperature by 20xc2x0 C. or more under a service condition of 105 hxc3x9714 kgf/mm2. The temperature of the gas impinged on each of the blades in the second and later stages is lower than that impinged on the first stage blade by a -temperature ranging from 50 to 100xc2x0 C.; however, the metal temperature of each of the second and later stage blades becomes higher as compared with the gas turbine of the class having the combustion temperature of 1300xc2x0 C. Accordingly, the material used for each of the second and later stage blades is required to exhibit a useful temperature of 600xc2x0 C. or more, and further, 800xc2x0 C. or more under a service condition of 105 hxc3x9714 kgf/mm2. If each blade is made from a material having a strength lower than that described above, the blade may be highly likely broken during operation, and it fails to sufficiently convert the energy of the gas flow into a rotating force, thereby reducing the efficiency.
The first stage nozzle, which initially receives combustion gas, is most frequently exposed to high temperature, and is subjected to significant thermal stress and thermal impact due to repetition of start-up and interruption of the gas turbine. For the gas turbines of the classes having the combustion gas temperatures of 1300xc2x0 C. and 1500xc2x0 C., the first stage nozzle may be made from an alloy having a useful temperature ranging from 700xc2x0 C. or more, and further 900xc2x0 C. or more under a service condition of 105 hxc3x976 kgf/mm2 even in consideration of the cooling ability. Each of the second and later stage nozzles is not severed in terms of temperature as compared with the first stage nozzle; however, since the metal temperature of each of the second and later stage nozzles becomes higher as compared with the gas turbine of the class having the combustion temperature of 1300xc2x0 C., each of the second and later stage nozzles may be made from a material having a useful temperature ranging from 600xc2x0 C. or more, and further 800xc2x0 C. or more under a service condition of 105 hxc3x9714 kgf/mm2.
According to the present invention, the turbine blades and turbine nozzles operated at the gas temperature at the inlet of the first stage turbine nozzle ranging from 1400 to 1650xc2x0 C., preferably, 1500 to 1650xc2x0 C. are preferably configured such that the first stage turbine blade and the first stage nozzle are each made from an Ni-based alloy having a single crystal structure and are each covered with a thermal insulation coating layer; the second stage turbine blade and the second stage turbine nozzle are each covered with an alloy coating layer; the Ni-based alloy having the single crystal structure contains, on the weight basis, 6-8% of Cr, 0.5-1% of Mo, 6-8% of W, 1-4% of Re, 4-6% of Al, 6-9% of Ta, 0.5-10% of Co, and 0.03-0.13% of Hf; and the Ni-based alloy having the single crystal structure further contains 0.1-2% of Ti and/or Nb. According to the present invention, the first stage blade and the first stage nozzle operated at the above gas temperature ranging from 1400 to 1495xc2x0 C. and the second turbine blade operated at the above gas temperature of 1500xc2x0 C. or more is preferably made from an Ni-based alloy having a columnar crystal structure containing, on the weight basis, 5-18% of Cr, 0.3-5% of Mo, 2-10% of W, 2.5-6% of Al, 0.5-5% of Ti, 0.05-0.21% of C, and 0.005-0.025% of B, and more preferably made from a unidirectionally solidified Ni-based alloy having a columnar crystal structure containing, in addition to the composition of the above Ni-based alloy, at least one kind of 1-4% of Ta, 10% or less of Co, 0.03-0.2% of Hf, 0.001-0.05% of Zr, 0.1-5% of Re, and 0.1-3% of Nb. In particular, the above Ni-alloy can be also used for the second, third or.fourth blades.
The second and third stage turbine nozzles are each preferably made from a Ni-based alloy having a polycrystalline structure containing, on the weight basis, 21-24% of Cr, 18-23% of Co, 0.05-0.20% of C, 1-8% of W, 1-2% of Al, 2-3% of Ti, 0.5-1.5% of Ta, and 0.05-0.15% of B.
To improve the heat efficiency of the gas turbine, as described above, it is most effective to increase the combustion gas temperature. If the metal temperature of the first stage turbine blade is set at a temperature of 920xc2x0 C. or more by making use of the high cooling technique for the blades and nozzles in combination of the heat insulation coating technique, the gas temperature at the inlet of the first stage turbine nozzle can be increased to a temperature ranging from 1450 to 1550xc2x0 C. This makes it possible to increase the power generation efficiency of the gas turbine 37% up or more. It should be noted that the power generation efficiency is expressed in LHV system. If the above gas turbine is operated in combination of the steam turbine as a combined power generation system further configured such that the turbine exhaust gas temperature is in a range of 590 to 650xc2x0 C., it is possible to provide a highly efficient combined power generation system capable of increasing the total power generation efficiency to 50% up or more, preferably, 55% up or more.
According to the present invention, it is possible to provide a gas turbine operated at a higher temperature, which is improved to increase the efficiency to 37% up or more in LHV at the turbine inlet temperature ranging from 1500 to 1650xc2x0 C.
(1) Long-blade Material
A long-blade material according to the present invention, which is made from a martensite based stainless steel containing 8-13 wt % of Cr, is preferably used for a final stage blade (rotating blade, the length of the blade portion: 30 inches or more, preferably, 40 inches or more, more preferably, 43 inches or more) of a high pressure-low pressure or high pressure-intermediate pressure-low pressure integral type steam turbine for 50 cycle power generation.
Further, the above martensite based stainless steel of the present invention is preferably used for a final stage blade (the length of the blade portion: 30 inches or more, preferably, 33 inches or more, more preferably, 35 inches or more) of a high pressure-low pressure or high pressure-intermediate pressure-low pressure integral type steam turbine for 60 cycle power generation.
The above martensite based stainless steel contains, on the weight basis, 0.08-0.18% of C, 0.25% or less of Si, 1.00% or less of Mn, 8.0-13.0% of Cr, 1.5-3% (preferably, more than 2.1 to 3% or less) of Ni, 1.5-3.0% of Mo, 0.05-0.35% of V, 0.02-0.20% of Nb and/or Ta in total, and 0.02-0.10% of N.
According to the high pressure-intermediate pressure-low pressure or high pressure-low pressure integral type steam turbine is preferably configured by mounting the above-described long-blades having a tensile strength of 120 kg/mm2 or more on a rotor shaft made from the martensite based heat-resisting steel which contains, on the weight basis, 0.18-0.28% of C, 0.1% or less of Si, 0.1-0.3% of Mn, 1.5-2.5% of Cr, 1.5-2.5% of Ni, 1-2% of Mo, and 0.1-0.35% of V, and which has structural properties in which the 105 h polished and notching creep rupture strengths (at 538xc2x0 C.) at the high pressure portion are 13 kg/mm2 or more; the tensile strength at the low pressure portion is 84 kg/mm2 or more; and the fracture surface transient temperature is 35xc2x0 C.
An erosion preventive layer is preferably provided on the leading edge portion of the final stage blade. The concrete length of the blade is represented by 33.5xe2x80x3, 40xe2x80x3, and 46.5xe2x80x3. The erosion preventive layer is made from a Co-based alloy containing, on the weight basis, 0.5-1.5% of C, 1.0% or less of Si, 1.0% or less of Mn, 25-30% of Cr, and 2.5-6.0% of W.
The long-blade of the steam turbine is required to have a high tensile strength and a high cycle fatigue strength for withstanding a high centrifugal strength and vibration stress caused by high speed rotation. From this viewpoint, since the fatigue strength of the blade material is significantly reduced if a harmful xcex4-ferrite phase is present in the metal structure of the blade material, the blade material must have such a composition as to exhibit a full-temper martensite structure.
The composition of the steel of the present invention is preferably adjusted such that the Cr equivalent calculated on the basis of the above-described equation becomes 10 or less so as to prevent the xcex4-ferrite phase from being substantially present in the metal structure of the steel.
The tensile strength of the long-blade material may be in a range of 120 kg/mm2 or more, preferably, 128 kgf/mm2 or more, more preferably, 128.5 kgf/mm2. The proof stress of the long-blade material may be in a range of 80 kg/mm2 or-more, preferably, 88 kg/mm2 or more. The elongation percentage is preferably in a range of 10% or more in the length direction and 5% or more in the peripheral direction, and the impact value thereof is preferably in a range of 3.45 kgf-m or more.
To obtain a homogeneous, high strength long-blade material for the steam turbine, the raw material is preferably subjected to refining heat-treatment. The heat-treatment is performed by heating the material having been produced by melting and forged to a temperature ranging from 1000 to 1100xc2x0 C. (preferably, 1000-1070xc2x0 C.) and keeping the material at that temperature, preferably, for 0.5-3 hr; quenching (preferably, oil-quenching) the material by rapidly cooling the material to room temperature; and tempering the material at a temperature ranging from 550 to 620xc2x0 C. Here, the tempering is preferably repeated twice or more. For example, a primary tempering is performed by heating the material at a temperature ranging from 550-570xc2x0 C., keeping the material at that temperature, preferably, for 1-6 hr, and cooling the material to room temperature;. and then a secondary tempering is performed by heating the material at a temperature ranging from 560-590xc2x0 C., keeping the material at that temperature, preferably, for 1-6 hr. and cooling the material to room temperature. The secondary tempering temperature is preferably set to be higher than the primary tempering temperature, preferably, by a temperature ranging from 10 to 30xc2x0 C., more preferably, 15 to 20xc2x0 C.
A final stage blade portion of the low pressure turbine according to the present invention, having the length of 914 mm (36xe2x80x3) or more, preferably, 965 mm (38xe2x80x3) or more, is applied to a 3600 rpm steam turbine for 60 cycle power generation, and a final stage blade portion of the low pressure turbine according to the present invention, having the length of 1041 mm (41xe2x80x3) or more, preferably, 1092 mm (43xe2x80x3) or more, more preferably, 1168 mm (46xe2x80x3) or more), is applied to a 3000 rpm steam turbine for 50 cycle power generation. In this case, the value of xe2x80x9cblade portion length (inch)xc3x97rotational speed (rpm)xe2x80x9d becomes 125,000 or more, preferably, 138,000 or more.
With respect to the long-blade material of the present invention, to adjust the alloy composition for obtaining a full martensite structure thereby ensuring a high strength, a high low-temperature toughness, and a high fatigue strength, the Cr equivalent calculated in accordance with the following equation.(the content of each element is expressed in wt %) is adjusted in a range of 4 to 10.
Cr equivalent=Cr+6Si+4Mo+1.5W+11V+5 Nbxe2x88x9240Cxe2x88x9230Nxe2x88x9230Bxe2x88x922Mnxe2x88x924Nixe2x88x922Co+2.5 Ta.
The content of C is preferably in range of 0.08% or more for obtaining a high tensile strength, and is preferably in a range of 0.2% or less for preventing the reduction of the toughness. In particular, the C content is preferably in a range of 0.10-0.18%, more preferably, 0.12-0.16%.
The elements Si and Mn are respectively added as a deoxidizer and a deoxidizer/desulfurizer upon melting of steel. The effect of adding Si or Mn can be obtained only by addition of a slight amount thereof. However, since Si is the element of assisting the generation of a xcex4-ferrite phase, the addition of a large amount of Si accelerates the generation of the xcex4-ferrite phase which exerts adverse effect in reducing the fatigue strength and the toughness of the material. Accordingly, the content of Si is preferably in a range of 0.25% or less. If the raw material is melted by a carbon vacuum deoxidizing process or an electro-slag melting process, it is not required to add Si, and it is rather desirable not to added Si. In particular, the Si content is preferably in a range of 0.10% or less, more preferably, 0.07% or less.
The addition of Mn in an amount of 0.9% or less is effective to improve the toughness. In particular, since Mn is effective as a deoxidizer, it may be added in a range of 0.6% or less, preferably, 0.1 to 0.5%, more preferably, 0.2-0.4% for improving the toughness.
Cr is effective to enhance the corrosion resistance and high-temperature strength; however, if Cr is added in an amount of more than 13%, it causes the generation of a xcex4-ferrite structure. On the other, if the content of Cr is less than 8%, the effect of enhancing the corrosion resistance and high-temperature strength cannot be sufficiently achieved. Accordingly, the Cr content is preferably in a range of 8 to 13%. In particular, the Cr content is preferably, in a range of 10.5-12.5%, more preferably, 11 to 12% from the viewpoint of improvement of the strength.
Mo is effective to enhance the tensile strength due to its function of reinforcing solid-solution and precipitation. Mo does not exhibit sufficient effect in improvement of the tensile strength and if Mo is added in an amount of more than 3% or more, it causes the generation of the xcex4-ferrite phase. Accordingly, the Mo content may be in a range of 1.5 to 3.0%, preferably, 1.8 to 2.7%, more preferably, 2.0-2.5%. In addition, W and Co each exhibit the same effect as that of Mo.
V and Nb are effective to precipitate carbides for enhancing the tensile strength and also to improve the toughness. The addition of V in an amount of 0.05% or less and Nb in an amount of 0.02% or less cannot sufficiently achieve the additional effect. The addition of V in an amount of 0.40% or more and Nb in an amount of 0.2% or more is undesirable because it causes the generation of the xcex4-ferrite phase. Accordingly, the V content is preferably in a range of 0.20 to 0.36%, more preferably, 0.25-0.31% and the Nb content is preferably in a range of 0.04 to 0.16%, more preferably, 0.06-0.14%. Ta may be added in place of Nb or in combination of Nb.
The addition of Ni in an amount of 2-3% is effective to enhance the low-temperature toughness, and to prevent the generation of the xcex4-ferrite phase. In particular, the Ni content is preferably in a range of 2.3 to 2.9%, more preferably, 2.4 to 2.8%.
The addition of N in an amount of 0.02-0.1% is effective to enhance the toughness and tensile strength, and to prevent the generation of the xcex4-ferrite phase. In particular, the N content is preferably in a range of 0.04 to 0.08%, more preferably, 0.045 to 0.08.
The reduction of Si, P and S is effective to enhance the low-temperature toughness without harming the tensile strength. Accordingly, it may be desirable to make the contents of Si, P and S as small as possible. To enhance the low-temperature toughness, the Si content is preferably in a range of 0.1% or less, more preferably, 0.05% or less; the P content is preferably in a range of 0.015% or less, more preferably, 0.010% or less; and the S content is preferably in a range of 0.015% or less, more preferably, 0.010% or less. The reduction of Sb, Sn and As is also effective to enhance the low-temperature toughness, and accordingly, it may be desirable to make the contents of Sb, Sn and As as small as possible. However, in consideration of the current steel-production technology, the content of Sb is limited to 0.0015% or less, preferably, 0.001% or less; the content of Sn is limited to 0.01% or less, preferably, 0.005% or less, and the content of As is limited to 0.02% or less, preferably, 0.01% or less.
Further, according to the present invention, the ratio Mn/Ni is preferably in a range of 0.11 or less.
The material of the present invention may desirably have a full-temper martensite structure by heat-treatment. The heat-treatment is performed by uniformly heating the material at a temperature ranging from 1000 to 1100xc2x0 C. to entirely transform the metal structure to an austenite structure; rapidly cooling (preferably oil-cooling) the material; heating and keeping the material to and at a temperature ranging from 550 to 570xc2x0 C. and cooling the material (primary tempering); and heating and keeping the material to and at a temperature ranging from 560 to 680xc2x0 C. and cooling the material (secondary tempering).
(2) Rotor Shaft for High Pressure-Low Pressure or High Pressure-Intermediate Pressure-Low Pressure Integral Type Steam Turbine
C is an element necessary for improving the hardenability and ensuring the toughness and strength with the content of 0.15%-0.4%. The content of C is preferably in a range of 0.20-0.28%.
Si and Mn have been added as a deoxidizer; however, according to the steel-production technology such as the vacuum carbon deoxidation process or electro-slag re-melting process, a good quality rotor can be produced by melting without addition of Si and Mn. To prevent embrittlement of the material caused after long-term use, the contents of Si and Mn should be reduced. The Si content may be in a range of 0.1% or less, preferably, 0.05% or less, more preferably, 0.01% or less, and the Mn content may be in a range of 0.5% or less, preferably, 0.05-0.25%, more preferably, 0.20% or less.
The addition of Mn in a trace amount is effective to fix an harmful element S, which degrades hot workability, as a sulfide MnS, that is, has an effect of reducing the adverse effect of S. Accordingly, in production of a large-sized forged product, such as a rotor shaft for the steam turbine, it may be desirable to add Mn in an mount of 0.01% or more. However, if the content of S can be reduced by the steel-production technology such as super-cleaning technology for reducing the contents of S and P, since the addition of Mn reduces the toughness and high-temperature strength, the content of Mn may be reduced to zero, if possible. In this embodiment, the Mn content is preferably in a range of 0.01 to 0.2%.
The addition of Ni in an amount of 1.5-2.7% is effective to improve the hardenability, creep rupture strength, and toughness. In particular, the Ni content is preferably in a range of 1.6 to 2.0%, more preferably, 1.7 to 1.9%. Further, to obtain the high-temperature strength in combination of the toughness, the Ni content may be set to be larger than the Cr content up to 0.20% or to be lower than the Cr content by 0.30% or less.
The addition of Cr in an amount of 1.5 to 2.5% is effective to improve the hardenability, toughness, and creep rupture strength, and to improve the corrosion resistance in steam. In particular, the Cr content is preferably in a range of 1.7 to 2.3%, more preferably, 1.9 to 2.1%.
The addition of Mo in an amount of 0.8 to 2.5% is effective to precipitate fine carbide particles in crystal grains during tempering and hence to improve the high-temperature strength and prevent the embrittlement due to tempering. From the viewpoint of improvement of the strength and toughness, the Mo content is preferably in a range of 1.0 to 1.5%, more preferably, 1.1 to 1.3%.
The addition of V in an amount of 0.15 to 0.35% is effective to precipitate fine carbide particles in crystal grains during tempering and hence to improve the high-temperature strength and toughness. In particular, the V content is preferably in a range of 0.20 to 0.30%, more preferably, more than 0.25% and not more than 0.30%.
Further, by adding any one of a rare earth element, Ca, Zr, and Al in producing the low alloy having the above composition by melting, the toughness can be improved. The content of the rare earth element is preferably in a range of 0.05 to 0.4%; the Ca content is preferably in a range of 0.0005 to 0.01%; the Zr content is preferably in a range of 0.01 to 0.2%; and the Al content is preferably in a range of 0.001 to 0.02%.
Oxygen exerts an effect on the high-temperature strength. According to the steel of the present invention, by controlling the content of O2 in a range of 5 to 25 ppm, it is possible to increase the creep rupture strength.
At least one of Nb and Ta is preferably added in an amount of 0.005 to 0.15%. If the total content of Nb and Ta is less than 0.005%, the effect to increase the strength cannot be-sufficiently achieved, while if it is more than 0.15%, for a large-sized structure such as a rotor shaft for the steam turbine, large carbides thereof are precipitated to reduce the strength and toughness. For this reason, the content of at least Nb and Ta is preferably in a range of 0.005 to 0.15%, more preferably, 0.01 to 0.05%.
The addition of W in an amount of 0.1% or more is desirable for enhancing the strength. However, if the W content is more than 1.0%, for a large-sized ingot, the strength is reduced due to segregation. Accordingly, the W content is preferably in a range of 0.1 to 1.0%, more preferably, 0.1 to 0.5%.
The ratio Mn/Ni is preferably in a range of 0.13 or less, or the ratio (Si+Mn)/Ni is preferably in a range of 0.18 or less. This limitation of ratio is effective to significantly prevent the embrittlement due to heating of an Nixe2x80x94Crxe2x80x94Moxe2x80x94V low alloy steel having a bainite structure usable for the high pressure-low pressure or high pressure-intermediate pressure-low pressure integral type rotor shaft. Further, by setting the ratio Ni/Mo in a range of 1.25 or more and the ratio Cr/Mo in a range of 1.1 or more, or setting the ratio Cr/Mo in a range of 1.45 or more and the ratio Cr/Mo in a range of a value defined by [xe2x88x921.11xc3x97(Ni/Mo)+2.78] or more, there can be obtained an advantage of achieving high strength in which the material heat-treated entirely under the same condition exhibits 105 h creep rupture strength (at 538xc2x0 C.) of 12 kg/mm2 or more.
Also, by setting the Ni content at a specific ratio to the Cr content, it is possible to ensure a higher strength on the high pressure side and to ensure a strength together with a higher toughness on the low pressure side.
The material used for the rotor shaft for the high pressure-low pressure or high pressure-intermediate pressure-low pressure integral type steam turbine of the present invention is preferably configured such that, at the high pressure portion or high pressure-intermediate pressure portion, the 105 h polished and notching creep rupture strengths (at 538xc2x0 C.) are each in a range of 13 kg/mm2 or more; and at the low pressure portion or intermediate pressure-low pressure portion, the tensile strength is in a range of 84 kg/mm2 or more and the fracture surface transient temperature is in a range 35xc2x0 C. or less. To obtain such excellent mechanical properties, the material is preferably subjected to tilting refining heat-treatment as follows. To make fine the metal structure, the material is preferably subjected to pearite treatment performed by keeping the material at a temperature ranging from 650 to 710xc2x0 C. for 70 hr or more prior to the refining heat-treatment.
* high pressure portion or high pressure-intermediate pressure portion of the rotor shaft: obtaining a large high-temperature strength
◯ quenching: heating and keeping the material to and at 930-970xc2x0 C. and then cooling it
◯ tempering: heating and keeping the material to and at 570-670xc2x0 C. and then slowly cooling it
(tempering is preferably repeated twice, and one tempering is preferably performed by heating and keeping the material to and at 650-670xc2x0 C.)
* low pressure portion or intermediate pressure-low pressure portion of the rotor shaft: obtaining a large tensile strength and low-temperature toughness
◯ quenching: heating and keeping the material to and at 880-910xc2x0 C. and then rapidly cooling it
◯ tempering: heating and keeping the material to and at 570-640xc2x0 C. and then slowly cooling it
(tempering is preferably repeated twice, and one tempering is preferably performed by heating and keeping the material to and at 615-635xc2x0 C.)
To be more specific, the material on the high pressure side is preferably quenched at a quenching temperature higher than that of the material on the low pressure side, to make the high-temperature strength higher than that of the material on the low pressure side, thereby obtaining a creep rupture time of 180 hr or more at 550xc2x0 C. and 30 kg/mm2 on the high pressure side; and the material on the low pressure side is preferably subjected to tilting heat-treatment such that the transient temperature at the center hole on the lower pressure side is lower than the high pressure side by 10xc2x0 C. or less. The tempering temperature of the material on the high pressure side is preferably set to be higher than that of the material on the low pressure side.
In the high pressure-low pressure integral type rotor shaft of the present invention, which is made from the above-described steel having a high creep rupture strength together with a high impact value, the final stage rotating blade (blade) having the length of 40 inches or more, preferably, 43 inches or more for 50 cycle power generation and 33 inches or more, preferably, 35 inches or more for 60 cycle power generation is preferably planted.
(3) Other Rotating Blades (Blades), Stationary Blades (Nozzles) and Others for Steam Turbine of the Present Invention
For the high pressure side blades, the first stage blade, or each of first, second and third stage blades is preferably made from a martensite steel containing, on the weight basis, 0.2 to 0.3% of C, 0.5% or less of Si, 1% or less of Mn, 10-13% of Cr, 0.5% or less of Ni, 0.5-1.5% of Mo, 0.5-1.5% of W, and 0.15-0.35% of V. For the low pressure side blades each having the length of 26 inches or less, each blade is preferably made from a martensite steel containing, on the weight basis, 0.05-0.15% of C, 0.5% or less of Si, 1% or less, preferably, 0.2-1.0% of Mn, 10-13% of Cr, 0.5% or less of Ni, and 0.5% or less of Mo.
The stationary blade (nozzle) of the present invention is preferably made from a tempering full-martensite steel containing, on the weight basis, 0.05-0.15% of C, 0.5% or less of Si, 0.2-1% of Mn, 10-13% of Cr, 0.5% or less of Ni, and 0.5% or less of Mo.
The casing of the present invention is preferably made from a Crxe2x80x94Moxe2x80x94V cast steel having a bainite structure containing, on the weight basis, 0.10-0.20% of C, 0.75% or less of Si, 1% or less of Mn, 1-2% of Cr, 0.5-1.5% of Mo, 0.05-0.2% of V, and 0.05% or less of Ti.